Fiber for reinforcing plastic composites and reinforced plastic composites therefrom

ABSTRACT

A high tenacity fiber for reinforcing plastic composites, the fiber being selected from the group consisting of polyester, aliphatic polyamide, and combinations thereof. The fiber is treated with a composition consisting essentially of an organofunctional silane in an amount sufficient to achieve 0.02 to 1.0 weight percent of the silane on the fiber, and a diluent which provides for the hydrolysis of the silane to a silanol. The fiber is used to reinforce a plastic composite additionally comprising a resin matrix.

This application is a division of application Ser. No. 624,897, filed6/27/84, now U.S. Pat. No. 4,748,197.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a high tenacity fiber for reinforcingplastic composites and to the composites themselves wherein thereinforcing fiber, selected from the group consisting of polyester,aliphatic polyamide and combinations thereof, has been treated with acomposition consisting essentially of an organo-functional silane in anamount sufficient to achieve 0.02 to 1.0 weight percent of the silane onthe fiber and a diluent which provides for the hydrolysis of the silaneto a silanol. More particularly, the present invention relates to a hightenacity, high elongation, low shrinkage polyester fiber which has beentreated with a composition consisting essentially of water andgamma-glycidoxypropyltrimethoxysilane in an amount sufficient to achieve0.02 to 1.0 weight percent of the silane on the fiber, especially foruse in reinforcing a composite wherein the resin matrix comprisesunsaturated polyester resin or other thermosetting or thermoplasticresins. The reinforcements can be used in bulk and sheet moldingcompounds, filament winding, pultrusion, spray-up and hand-layup.

2. The Prior Art

A composite consists of basically three major elements: the resinmatrix, the reinforcement dispersed in the matrix, and thereinforcement-resin matrix interface. Synthetic fibers in staple orfilamentary form, and fabrics produced therefrom, are known for polymerreinforcement. Typical of the fibrous reinforcements are glass,polyester, polyamide (nylon and aramid) and polyolefin fibers.Conventional matrix resins include thermoplastics, such as nylon andpolyolefins, and thermosetting materials, such as epoxy and unsaturatedpolyester resins. Since the primary function of the fiber matrixinterface is to transmit stress from the matrix to the reinforcingfibers, the chemical and physical features of the interface are criticalto the mechanical properties and end use performance of the composite.The compatability between the reinforcing fiber and matrix is then adetermining factor in the load sharing ability of the composite. Fibercoatings/binders have been used to enhance the compatability of thereinforcing fibers and resins with which they are to be used. See, forexample, U.S. Pat. No. 3,637,417 to Green, hereby incorporated byreference. It is known to utilize silane coupling agents to bonddissimilar materials such as organic polymer and fibrous glass in thefield of reinforced plastics. See, e.g., Green, supra, U.S. Pat. No.4,158,714 to Brichta et al., and U.S. Pat. No. 3,658,748 to Andersen etal., and Marsden and Sterman, HANDBOOK OF ADHESIVES, Second Edition, 40,640 (1977), all of which are hereby incorporated by reference. It isalso known to utilize silane coupling agents to improve fiber to rubberadhesion, as taught by Japanese Kokai Publication J53-024423, herebyincorporated by reference, wherein a polyethylene terephthalate yarn iscombined with from 0.7 to 1.2 weight percent on the yarn of a liquidcomposition consisting essentially of 10 to 30 weight percent of asilane having the structural formula ##STR1## wherein n is 2 to 5, up toone weight percent of a nonionic wetting agent and 70 to 90 weightpercent water. The present invention, however, is directed towardsreinforcement of plastic composites and not elastomeric structures.

It is also conventional to substitute organic synthetic fibers in wholeor in part for glass fibers in reinforced plastics. Some advantages arepointed out in U.S. Pat. No. 3,639,424 to Gray et al., herebyincorporated by reference, wherein heatset polyester staple is used toreinforce thermoplastic/thermosetting polymers for improved impactstrength. Heatsetting the fiber allegedly permits uniform fiberdispersion in molded products.

The use of chemically modified polyester fabric as an auxiliaryreinforcing agent with glass fibers for thermosets, including polyester,vinyl ester and epoxy, for improved impact resistance and flexuralstrength over straight glass reinforcement is disclosed in PlasticsWorld Magazine, November, 1980, Volume 38, No. 11, page 102, herebyincorporated by reference.

Japanese Kokai Publication 54-55077 discloses a method for adhesion ofpolyester fiber/fabric and unsaturated polyester resins throughapplication of a latex, which preferably includes a small quantity ofbisphenol epoxy resin, to the polyester fiber/fabric.

The present invention is directed towards improving compatabilitybetween a resin matrix and the reinforcing fibers to thereby enhance thereinforced composite properties.

SUMMARY OF THE INVENTION

The present invention provides a high tenacity reinforcing fiberselected from the group consisting of polyester, aliphatic polyamide andcombinations thereof, for reinforcing composites. The fiber may bestaple or continuous filament per se or a knitted, woven or nonwovenfabric or mats. The reinforcing fiber is treated with a compositionconsisting essentially of an organofunctional silane in an amountsufficient to achieve 0.02 to 1.0, preferably 0.1 to 0.5, weight percentof the silane on the fiber, and a diluent which provides for thehydrolysis of the silane to a silanol. Wettability of the fiber andadhesion of the fiber to a resin matrix are thereby enhanced, and thecompatibility of such reinforcing fiber to the resin is improved so thatcomposites with reinforcement uniformly dispersed therein can befabricated.

It is preferred that the treating composition consist essentially of 1to 50, preferably 3 to 25, weight percent of the silane; up to 1 weightpercent of a wetting agent; and 49 to 99, preferably 74 to 97, weightpercent of the diluent.

The preferred diluent is water although it is believed that aqueoussystems containing other highly polar materials such as low molecularweight alcohols would be satisfactory. The preferred wetting agent isnonionic, e.g., polyoxyalkylene nonylphenols, octylphenoxyethanols,although anionic wetting agents such as the dialkylsufosuccinates,particularly dinonyl and dioctyl), and 2-ethylhexylphosphate aresuitable.

Organofunctional silane coupling agents may be found in chapter 40 ofthe HANDBOOK OF ADHESIVES, supra. The organofunctional silane utilizedin the present invention is preferably selected from the groupconsisting of: Vinyl-tris(beta-methoxyethoxy) silane,gammaMethacryloxyalkyltrialkoxysilane,beta(3,4-Epoxycyclohexyl)alkyltrialkoxysilane,gamma-Mercaptoalkyltrialkoxysilane, gamma-Aminoalkyltrialkoxysilane,N-beta(aminoethyl)-gamma-aminoalkyltrialkoxysilane, and ##STR2## whereinn is 2 to 5, and combinations thereof. The most preferred silane isgamma-glycidoxypropyltrimethoxy silane.

The preferred reinforcing polyesters are the linear terephthalatepolyesters, i.e., polyesters of a glycol containing from 2 to 20 carbonatoms and a dicarboxylic acid component containing at least about 75percent terephthalic acid. The remainder, if any, of the dicarboxylicacid component may be any suitable dicarboxylic acid such as sebacicacid, adipic acid, isophthalic acid, sulfonyl-4,4'-dibenzoic acid,2,8-dibenzofuran-dicarboxylic acid, or 2,6-naphthalene dicarboxylicacid. The glycols may contain more than two carbon atoms in the chain,e.g., diethylene glycol, butylene glycol, decamethylene glycol, andbis-(1,4-hydroxymethyl)cyclohexane. Examples of linear terephthalatepolyesters which may be employed include poly(ethylene terephthalate),poly(ethylene terephthalate/5-chloroisophthalate)(85/15), poly(ethyleneterephthalate/5-[sodium sulfo]-isophthalate) (97/3),poly(cyclohexane1,4-dimethylene terephthalate), andpoly(cyclohexane-1,4-dimethylene terephthalate/hexahydroterephthalate)(75/25).

Suitable reinforcing polyamides include, for example, those prepared bycondensation of hexamethylene diamine and adipic acid, condensation ofhexamethylene diamine and sebacic acid known as nylon 6,6 and nylon6,10, respectively, condensation of bis(para-aminocyclohexyl)methane anddodacanedioic acid, or by polymerization of 6-caprolactam,7-aminoheptanoic acid, 8-caprylactam, 9-aminopelargonic acid,11-aminoundecanoic acid, and 12-dodecalactam, known as nylon 6, nylon 7,nylon 8, nylon 9, nylon 11, and nylon 12, respectively.

The most preferred reinforcing fiber is a polyethylene terephthalate,characterized by a thermal shrinkage of up to about 11 percent,preferably 3 percent or less; an elongation of from about 10 to 28,preferably 14 to 24 percent; a modulus after cure of at least about 60,preferably 70 to 90 grams per denier; and a tenacity of at least 5.5,preferably 7 to 9 grams per denier. By modulus after cure is meant themodulus of the fiber after exposure in an unconstrained state to curingtemperatures for the composite.

The present invention also relates to a fiber reinforced plasticcomposite comprising a resin matrix and the described reinforcing fiber.

The resin matrix may include thermosetting or thermoplastic (includingpolyolefin) resins. Suitable thermosetting resins include polyester(preferably unsaturated), epoxy, or vinyl ester resin systems. Suitablethermoplastic resin systems include polyvinyl chloride, polyethylene,polypropylene, polystyrene, polyvinyl alcohol, polyamide, polyurethane,etc.--any thermoplastic having a lower melting point than that of thefiber, e.g., less than 230° C. for reinforcement with polyester fibersand less than 200° C. for reinforcement with nylon fibers.

The resin matrix also may include enhancers, mold release agents andfillers, as are known in the composite art, in addition to the treatedfibers and resins.

It is also preferred that there be other reinforcing fibers, morepreferably glass fibers, as will be more fully discussed below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph depicting the effect of thermal exposure on (a)shrinkage and (b) fiber modulus;

FIG. 2 is a graph depicting the effect of fiber length and loading oncomposite properties;

FIG. 3 schematically shows the equipment utilized to evaluateinterfacial shear strength;

FIG. 4 is a graph depicting the effect of interfacial shear strength oncomposite properties;

FIGS. 5a-b are photographs of an adhesion test sample;

FIG. 6 is a graph depicting the effect of fiber loading on compositeproperties; and

FIGS. 7A-D are bar graphs of BMC injection molded composite properties.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Preliminary research was directed towards engineering a polyethyleneterephthalate (hereafter PET) fiber specifically for reinforcement ofrigid composites. Research first addressed the question of what type ofPET fiber is most suitable as a reinforcing fiber in composites. Thereare many grades of PET commercially available. However, preliminaryscreening showed only very specific types to be even potentially usefulin composites.

With reference to Table I, it can be seen that textile grade PET fiber(Burnet Southern, Inc.) is unsuitable for reinforcement, primarilybecause of its low tenacity, low modulus, and large thermal shrinkage,resulting in a composite with poor notched impact strength.

It was expected that high tenacity industrial PET fibers could providesuperior impact strength with adequate tensile strength. Preliminarywork showed this to be true; however, a wide range of values wasobtained based on differing fiber types. It has been found that tensileproperties of the fiber as normally measured, as well as after exposureto the thermal molding conditions encountered in fabricating areinforced composite article, are important. The latter is moreimportant since the final properties of the fiber in the composite moredirectly affect composite performance.

EXAMPLE 1

Data for three types of high strength industrial PET fibers,commercially available from Allied Corporation, are shown in Table 1.These are: Type A--a high tenacity, low elongation fiber normally usedfor tire reinforcement; Type B--a high tenacity, high elongation, lowshrinkage fiber normally used for hose reinforcement; and Type C--a hightenacity, high elongation, ultralow shrinkage fiber normally used forcoated fabrics. Molded composite specimens were prepared from each ofthe fibers using a 12 weight percent PET fiber loading, equivalent involume to 20 weight percent glass. The type B fiber appeared to give thebest balance of composite properties. This is unexpected based oninitial fiber properties.

The fibers were subjected to simulated curing temperatures of from95°-150° C. while in an unconstrained state. Fiber physical propertieswere measured both before (control) and after heat treatment. Theeffects of thermal exposure on Fibers A, B and C, respectively arepresented in Tables 2-4.

As shown in FIG. 1-a, Type A underwent a large amount of shrinkage attemperatures as low as 120° C. In contrast, the two low shrinkage fibersB and C showed very little shrinkage during thermal exposure, asexpected. Since excessive shrinkage during processing would have adetrimental effect on fiber/resin bonding, this might be expected toresult in reduced composite properties.

The thermal exposure also had greatly differing effects on the moduli ofthe different fibers tested (reference FIG. 1-b). When tested at roomtemperature, the high tenacity Type A fiber had a 20-25 percent higherinitial modulus and 10 percent higher tenacity than the low shrinkfibers. However, after exposure to the elevated temperatures, the Type Afiber showed a more dramatic change than either of the others. Also, andnot to be expected from normal measured physical properties, the finalmodulus of Type A was nearly 30 percent lower than the final modulus ofthe two low shrink fibers after exposure to 150° C. Therefore, in theireffect on composite properties, the two low shrinkage fibers appear tobe superior in spite of the fact that tensile properties on virgin yarnappear to be superior for the Type A fiber.

The ultralow shrink Type C fibers tested had a lower molecular weight,which results in a lower tensile strength fiber than the Type B lowshrink fiber. It was found that the initial tenacity was essentiallyunchanged by thermal treatment for any of the fibers. Therefore, theslightly better dimensional stability of the Type C ultra low shrinkfiber is more than offset by the higher tenacity Type B low shrinkfiber.

                                      TABLE 1                                     __________________________________________________________________________    Fiber and Composite Properties.sup.1                                                 Fiber Properties    Composite.sup.1 Properties                                               Thermal                                                                            Notched                                                                            Tensile                                              Tenacity.sup.4                                                                     Modulus.sup.5                                                                      Elonga-                                                                            Shrink-                                                                            Impact                                                                             Strength                                                                           Flexural                                 Fiber  gpd  gpd  tion, %.sup.6                                                                      age, %.sup.7                                                                       ft lb/in.sup.8                                                                     psi.sup.9                                                                          psi.sup.10                               __________________________________________________________________________    E-Glass                                                                              6.5  320  2.1  0    4.4  5000 15 200                                   Textile Fiber.sup.2                                                                  4.5  30-40                                                                              30   5-8  2.9  2900 2500                                     Type A.sup.3                                                                         8.9  123  14   9.1  8.4  2500 4100                                     Type B.sup.3                                                                         8.1   98  22   1.8  9.7  2900 4300                                     Type C.sup.3                                                                         7.6   99  21   0.6  9.4  2700 4400                                     __________________________________________________________________________     .sup.1 Polyester BMC formulation 20 weight percent glass, glass replaced      by PET on equal volume basis Fiber length = 0.25 inch (0.64 cm) Balance       18.33% isophthalic polyester resin (MR 14017 USS Chemicals), 5.86%            resinous modifier (MR 63004 USS Chemicals), 0.31% tertbutyl(perbenzoate),     0.12% promoter, 0.01% inhibitor solution (butylated hydroxy toluene and       styrene), 1.30% zinc stearate, 52.57% aluminum trihydrate, 1.50% pigment      (CM7106 Red by Plastic Colors).                                               .sup.2 Commercially available from Burnet Southern.                           .sup.3 Commercially available from Allied Corporation.                        .sup.4 ASTM D885.                                                             .sup.5 ASTM D885.                                                             .sup.6 ASTM D885.                                                             .sup.7 ASTM D885.                                                             .sup.8 ASTM D256                                                              .sup.9 ASTM D638                                                              .sup.10 ASTM D790                                                        

The optimum PET fiber length for staple reinforcement appears to be thelongest length which will still allow practical handling and dispersion.Notched impact strength showed a significant response to fiber length.Three fiber lengths, 1/8, 1/4 and 1/2 inch (0.32, 0.64 and 1.3 cm) wereused to determine the affect of PET fiber length at several levels oftotal fiber loading. Results are plotted in FIGS. 2a and b. For eachdoubling of fiber length the impact strength also doubled. Subsequenttesting showed that a 3/4 inch (1.9 cm) PET fiber reinforced compositeresulted in still more improved impact strength. There was littledifference in composite tensile strength between 1/8 and 1/4 inch (0.32and 0.64 cm) fiber. However, using 1/2 inch (1.3 cm) fiber resulted inan increase in tensile strength of about 50 percent. These results pointout a significant advantage of an organic filament reinforcement. Incontrast to glass, which can shatter into shorter lengths duringcompounding, PET fiber does not break into shorter lengths. This allowsPET fiber to retain its maximum advantage for impact strength.

EXAMPLE 2

It is known that the fiber coating is a factor in stress distributionfor the composite. In preliminary studies it was observed by scanningelectron microscope that a very nonuniform wetout and poor adhesion wereachieved between PET fibers and thermoset polyester resins. To improvethese features for thermoset polyester resins various types of fibercoatings were used. The properties of these coatings were varied inorder to determine the degree of influence of the boundary on thecomposite performance.

The binders applied are listed in Table 5. The yarn utilized was Type Bof Table 1. Yarn was removed from a supply package at 1000 ft/min (305m/min) and passed over a stainless steel lube roll that was partiallyimmersed in the binder/finish composition, after which the yarn waspassed through drive rolls and thence to a winder where it was wound.The yarn was removed from the supply package through eyelet guides andtwo tension gates to flatten the yarn bundle for passage over the rolland to prevent bouncing. The yarn touched the roll as a tangent, aminimum contact angle being maintained. The lube roll was 4 inches (10cm) in diameter and turning at an RPM sufficient to achieve the percentsolids on yarn indicated in Table 5. For the composition of the presentinvention, the roll was turning at 15 RPM.

Several methods to determine the adhesive properties of the PET fiberwere evaluated. For comparison and evaluation purposes, the adhesiveproperties were measured as a function of the interfacial shearstrength. The interfacial shear strength was calculated from the pulloutload, P using the following equation ##EQU1## where τ=interfacial shearstrength,

D=fiber diameter, and

L=embedded fiber length in the matrix.

A small portion of an overfinished PET fiber was embedded to a depth of0.25 inch (0.64 cm) in a compounded thermoset polyester resin of theformulation set forth in Table 1. FIG. 3 depicts the setup for theoperation utilized to evaluate the interfacial shear strength. The fiber11 was subjected to a tensile force (pullout force) with an Instron 12in the axial direction of the filaments, causing shear debonding stresson the interface. The Instron 12 has a recorder 13 attached thereto torecord the pullout load, P, in pounds (kg). By using this technique, theeffect of use of different binders on the interfacial strength of thecomposite could be determined. This test is called the button moldpullout test. The interfacial shear strength is the total overallstrength of the interface due to physical, mechanical and chemicalbonding. The composite physical properties were determined for thedifferent interfacial shear strength values delivered by the differentbinders, and the effect is depicted in FIG. 4. As expected, up to alevel of about 7.3 kg/cm³, composite properties improved proportional toτ; however, at just over 7.3 kg/cm³ the data seem to show that maximumcomposite properties were achieved and further increases in interfacialshear strength were detrimental. In fact, what was observed is that thetype of materials which achieve a high concentration of crosslinkingsites and therefore a very high interfacial shear strength showed a poorwetout by the resin. This poor resin wetout created a number of voidsand flaws which acted as stress concentrators within the matrix leadingto early failure. Thus, fiber/matrix wettability is also a key to betterload sharing and transferring between phases.

The wettability of the treated fibers listed in Table 5 by the specifiedresin was determined as follows. A value of 1 to 10 was assigned to aparticular fiber wherein 1=poor and 10=excellent based on visualinspection and two tests. The visual examination occurred during BMCcompounding of 1/2 inch (1.3 cm) length PET filament (1000 denier, 192filaments) at 20 percent loading (i.e., volume equivalent 20 weightpercent fiberglass) with the resin matrix set forth before. The resinmatrix included 1.5 weight percent of a red pigment available as CM-7106from Plastic Colors to aid the visual inspection. After compounding for60 seconds, the compounded mass was manually pulled apart, fibers pulledout and felt for wetness and observed for color change. Compounding wasrestarted and continued for 30 seconds after which the same observationswere made. This continued until maximum wetout of the fiber occurred.For fibers with binder systems 2 and 5 (Table 5) the visual inspectionalso included examination of the fiber bundle for spreadability andpickup of the resin during a filament winding process when the fiberbundles were run in parallel and with minimal tension under a roll in aresin bath; the resin was a polyester resin (50 parts Freeman 40-2092and 52 parts Freeman 40-2490). Fiber with binder system 5 had a vastlygreater pickup than fiber with binder system 2. One of the tests reliedupon in forming the wettability value was using a scanning electronmicroscope (SEM) to evaluate broken composites. The fibers of Table 5were used to compound a 20 percent load PET fiber reinforced BMCcompound. These compounds were molded [320° F. (160° C.), 1.5 min, 1 tonpress] into tensile, flexural and impact specimens, as well as plaques.The specimens were broken for testing in accordance with ASTM tests: thetensile specimen according to D-638, the flexural according to ASTMD-790 and the impact specimen according to ASTM D-256. The plaques weremanually broken. The broken specimens and plaques were taken to an SEMlaboratory for examination. The fibers jutting out from the fracturepoint were observed for residual matrix or matrix cling. If the fiberwas clean, adhesion and wetout were ranked 1. The more matrix clingingto the fiber, the higher the ranking, up to a rating of 10. Button testspecimens could be similarly evaluated. SEM photographs, the buttonsample and the pulled out fiber are shown in FIG. 5. FIG. 5-a shows thesection of the fiber that was embedded where pieces of the matrix clingto the fiber. FIG. 5-b shows the orifice from which the fiber waspulled. SEM rankings are presented in Table 6. In another test thecontact angle of a polyester molding resin (MR14017 from USS Chemicals)on a unidirectional fabric made with the coated yarns was measured. Theunidirectional fabric was made by guiding the coated PET fiber bundlesover a winding mechanism so that a fabric could be made from closelypacked parallel fiber bundles. A sessile drop of the liquid moldingresin was placed on the fabric held under tension (0.2 gram/fil), andthe contact angle on the fabric was measured with time. The contactangles measured are presented in Table 6 as well as a ranking of thecoated fibers with respect to wettability.

PET fiber inherently has low fiber bundle integrity (fiber bundleintegrity is the degree to which the individual filaments adhere to eachother). The main benefit of a low integrity fiber is that it allows thedispersion of single filaments over a large resin matrix area. This evendistribution results in a homogeneous reinforced composite, a directresult of which is an improved cosmetic look.

The binder system of the present invention (number 5 of Table 5) waschosen as the low integrity system because of its good adhesion andexceptional resin wetout. This was despite the fact that fiber withbinder system 2 resulted in a composite with equal or better physicalproperties. See Table 7. Note that the major difference between bindersystems 2 and 5 is the additional oils in the noncontinuous phase forsystem 2, i.e., both systems include the same epoxy silane and water.However, these benefits could not offset the exceptional resin wetout ofthe fiber with binder system 5 during processing, as observed duringfilament winding operations. This increase in wettability was also seenin BMC processing in the form of improved mixing and surface appearance.In addition, the BMC composite physical properties for the fiber withbinder system 5 were acceptable. The binder wettability characteristicswere also measured via contact angle and again, fiber with binder system5 showed a major edge over the balance of the system. Fiber with bindersystem 2, when used in forming a BMC plaque, evidenced white, dry spotsof yarn in the plaque, which were aesthetically unacceptable. This iscritical, given the market for such composites.

EXAMPLE 3

Several thermoset polyester resins were evaluated to determine the bestfor composite applications where 0.5 inch (1.3 cm) PET fiber coated with0.2 weight percent solids of binder system 2 was used as reinforcingfiber, alone and in combination with glass. A sample with 100 percentglass reinforcement was also run. Total fiber loading was kept constantat the volume equivalent to 20 weight percent glass. The curingtemperature used was 300° F. (149° C.). Typical composite physicalproperties were measured on the molded samples, and are shown in Table8. Resin matrix formulation was as previously described, with the resinsidentified in Table 8.

Impact strength is a measure of a composite's resistance to a suddensharp impact. Replacement of glass fiber by polyester fiber results in agreat improvement in this property. Two types of impact tests were run,notched and unnotched. In the notched impact test, impact strength for100 percent PET fiber reinforced composite increased from 15 to 20 footpound/inch as the resin elongation was increased from 0.9 percent to 10percent. For the 100 percent glass reinforced composite and compositesreinforced by mixtures of PET fibers and fiberglass, impact strengthremained relatively constant with increasing resin elongation. As theproportion of PET fiber was increased, the impact strength was seen toincrease at all resin elongations. The increase was greater at thehigher resin elongations. Results of the unnotched impact test showedthe same general trends observed in the notched test. In this case,however, the composites were reinforced by 100 percent glass fibers, andPET/glass fiber mixtures tended to lose impact strength as resinelongation increased. Again, as the proportion of PET fiber and thereinforcing fiber increased, impact strength increased at all resinelongations with the increase being larger at higher elongations. Theseresults demonstrate that higher elongation resins are preferable forincreased impact strength for PET fiber reinforced composites.

While PET is stronger than glass on a strength per unit weight basis(9.0 gpd versus 6-8 gpd), the fact that a specific gravity is nearly 50percent lower than glass means that an equivalent volume of PET fiberswill be less strong than glass fibers. Thus, PET reinforcing fibersprovide a molded part which is not as strong as that reinforced by 100percent glass fibers.

On an equal volume loading basis, composite strength decreased roughlyby a factor of 2 going from 100 percent glass fiber reinforced compositeto a 100 percent PET fiber reinforced composite. The change in tensilestrength with PET/glass fiber ratio showed a linear relationship in allresin systems, indicating that composite strength followed the rule ofmixtures well.

Tensile strength did not change dramatically with resin elongation. Ingeneral, the maximum value occurred using the 6.1 percent elongationresin, with the tensile strength being 10 to 25 percent higher than forthe high and low elongation resin. The PET/glass ratio of thereinforcing fiber used did not appreciably affect the location of thismaximum. Therefore, the 6.1 percent elongation resin appears to be theresin of choice to maximize the tensile strength of PET reinforcedcomposites.

Flexural strength is another measure of the strength of a compositematerial, having both tensile and compressive components. The samegeneral trends were seen here that were noted for tensile strength. For100 percent PET fiber and 100 percent glass fiber reinforced compositesthe maximum tensile strentgh was obtained using the 6.1 percentelongation resin. This was also the case for the sample reinforced by a12.5/87.5 PET/glass fiber mixture. The samples reinforced by 25/75 and50/50 PET/glass fiber mixtures showed a steady increase in flexuralstrength with increasing resin elongation. Flexural strength gains of 10to 30 percent were obtained by using the 6 or 10 percent elongationresins relative to the 0.9 percent elongation resin typically used with100 percent fiberglass reinforced composites. Therefore, the use of amedium to high elongation resin is preferable to maximize flexuralstrength.

With the exception of Barcol hardness, increasing the resin elongationover that typically used (0.9%) with glass fiber resulted in improvedcomposite physical properties. Tensile and flexural strength had themaximum values using a resin with a 6.1 percent elongation to break.This medium elongation resin thus appeared to be the best for use withthe PET fiber coated with a binder system.

EXAMPLE 4

As generally recognized, the mechanical properties of a reinforcedcomposite are strongly dependent on the level of reinforcing fiber used.In general, the properties improve with total fiber loading up to amaximum loading where the mechanical properties level or fall off due toinadequate fiber dispersion or insufficient resin to form a good matrix.

In this example BMC formulations were made using 100 percent of PETfiber coated with binder system 2, 100 percent glass fiber, and mixturesof the PET fiber and glass fiber as the reinforcing agent. Fiberloadings were reported as the weight percent glass equivalent to thetotal fiber volume loading used. Total fiber loadings of 10 to 35percent were used. Sample specimens were made and tested for tensilestrength and impact strength. See Table 9.

With each reinforcing system the impact strength increased withincreasing fiber loading, as shown in FIG. 6. The best impact strengthswere seen for the composites reinforced with 100 percent PET fiber,having values as high as 21 foot pound/inch. Impact strengths for thePET/glass fiber mixtures were in between the values for the 100 percentreinforced composites and the 100 percent glass fiber reinforcedcomposites.

For this BMC formulation, total fiber loading equivalent to about 25percent by weight fiberglass appeared to be optimum. Beyond this level,difficulties began to be encountered in compounding, while only smalladditional gains in impact strength were seen.

Tensile strengths also increased with increasing total fiber loading foreach of the reinforcing systems studied and as shown in FIG. 6. PETfiber is as strong as glass fiber on a weight basis, but because of thehigher density of glass, glass reinforced composites are stronger on anequal volume reinforcement basis. However, at the 20-25 percent loadinglevel, the composites reinforced by PET/glass fiber mixtures were nearlyas strong as the 100 percent glass reinforced composites.

EXAMPLE 5

In this example bulk molding compounds containing 20 weight percentglass loading, glass replaced by PET fiber on equal volume basis, weremade and molded into specimens for testing. The BMC resin matrix was aspreviously described, and the PET fiber had been treated with bindersystem 2. The composition of the reinforcing fibers was varied, withrelative polyester fiber/glass fiber volume ratios of 0/100, 25/75,50/50, and 100/0 being used. All fiber loading levels reported are givenas the weight percent glass equivalent to the particular volume ofloading of the fiber used. The same composite properties were measuredas reported previously and the results are given in Table 10. These datashow that partial replacement of glass fiber by PET fiber in areinforced composite results in significant gains in impact strengthwith very little sacrifice in tensile strength, especially at a fiberratio of 25/75 PET/glass. This results in molded parts with overallproperties which are superior to parts reinforced by either fiber usedalone.

Studies were also run on BMC injection molded composites reinforced byall PET fiber, all glass fiber, and PET/glass fiber mixtures todetermine the effect. The results are presented in Table 11 and showngraphically in FIGS. 7A-D.

The replacement of glass fibers by PET fibers resulted in greaterincreases in impact strength than were observed for compression moldedsamples. At the same time, tensile strength and flexural strength wereless effective by replacement of glass with PET fibers than incompression molded samples. This is presumably due to the fact thatshear and the injection molding machine broke the glass fibers intoshorter lengths without affecting the lengths of the PET fibers. Inaddition, it may be possible that the presence of the PET fibers protectthe glass fibers from damage to some extent.

EXAMPLE 6

Binder systems are formulated similar to that of system 5, butsubstituting the following organofunctional silanes for the silane ofsystem 5:

Vinyl-tris(beta-methoxyethoxy)silane;

gamma-Methacryloxyalkyltrialkoxysilane;

beta(3,4-Epoxycyclohexyl)alkyltrialkoxysilane;

gamma-Mercaptoalkyltrialkoxysilane;

gamma-Aminoalkyltrialkoxysilane; and

N-beta(aminoethyl)-gamma-aminoalkyltrialkoxysilane.

These systems are used to overfinish type B (Table 1) PET fibers forreinforcement of plastic composites. Performance should be comparable toPET fiber treated with binder system 5.

EXAMPLES 7-8

PET fiber type B with binder system 5 at 0.20% solids pickup was cutinto 3/4 and 1 inch (1.9 and 2.5 cm) lengths in Examples 7 and 8,respectively, and used to compound a 20 percent load, 100 percent PETfiber reinforced BMC compression compound with the resin matrixformulation of Table 1 (6.1% elongation resin). Excellent compositeproperties were obtained.

EXAMPLE 9

Nylon 6 fiber having a nominal denier of 1260, 204 filaments, modulus of44, breaking strength (lbs) 24.5, tenacity 8.8 gpd, breaking elongation(%) 20.5, commercially available from Allied Corporation, had bindersystem 5 applied via a kiss roll at a solids pickup of 0.20 percent. Thefiber was cut into 0.5 inch (1.3 cm) lengths and used to compound a 20percent load nylon reinforced BMC compression composite with the resinmatrix formulation of Table 1. Composite properties are presented inTable 11.

                  TABLE 2                                                         ______________________________________                                        Effect of Thermal Exposure on Fiber A                                                        Thermal           Elonga-                                      Exposure                                                                              Time   Shrinkage,                                                                              Tenacity,                                                                             tion   Modulus                               Temp. ° C.                                                                     Min.   percent   gpd     Percent                                                                              gpd                                   ______________________________________                                        --*     --     9.1       8.8     13.1   123.2                                  95     1      8.8       9.0     13.2   114.9                                  95     3      8.5       9.3     13.7   112.8                                  95     10     9.2       8.8     14.0   105.2                                  95     20     8.4       9.1     14.6   106.6                                 120     1      5.6       9.3     18.6   95.6                                  120     3      6.0       9.2     19.5   85.2                                  120     10     4.8       9.2     20.4   85.9                                  120     20     4.4       9.0     20.2   82.4                                  150     1      1.1       8.7     26.1   62.4                                  150     3      0.2       8.6     28.2   63.8                                  150     10     0.6       9.0     27.6   65.2                                  150     20     0.2       8.9     28.8   62.4                                  ______________________________________                                         *Control                                                                 

                  TABLE 3                                                         ______________________________________                                        Effect of Thermal Exposure on Fiber B                                                        Thermal           Elonga-                                      Exposure                                                                              Time   Shrinkage,                                                                              Tenacity,                                                                             tion   Modulus                               Temp. ° C.                                                                     Min.   percent   gpd     Percent                                                                              gpd                                   ______________________________________                                        --*     --     1.8       8.1     22.1   97.8                                   95     1      1.5       8.0     21.7   91.2                                   95     3      1.4       8.1     22.0   92.2                                   95     10     1.6       7.9     20.9   93.6                                   95     20     1.3       7.9     21.6   89.8                                  120     1      1.1       7.9     22.0   88.1                                  120     3      1.0       8.0     22.2   88.4                                  120     10     0.9       7.9     22.6   86.3                                  120     20     0.9       7.9     22.4   86.3                                  150     1      0.3       7.8     23.6   84.6                                  150     3      0.0       7.9     24.9   77.8                                  150     10     0.1       7.7     23.8   81.1                                  150     20     0.0       7.9     25.4   76.6                                  ______________________________________                                         *Control                                                                 

                  TABLE 4                                                         ______________________________________                                        Effect of Thermal Exposure on Fiber C                                                        Thermal           Elonga-                                      Exposure                                                                              Time   Shrinkage,                                                                              Tenacity,                                                                             tion   Modulus                               Temp. ° C.                                                                     Min.   percent   gpd     Percent                                                                              gpd                                   ______________________________________                                        --*     --     0.6       7.6     20.7   99.1                                   95     1      0.3       7.1     20.5   91.5                                   95     3      0.2       7.2     20.9   91.5                                   95     10     0.3       7.4     21.0   90.1                                   95     20     0.1       7.5     21.1   89.4                                  120     1      0.0       7.6     22.0   90.8                                  120     3      0.0       7.5     21.6   92.2                                  120     10     0.0       7.5     21.9   88.0                                  120     20     0.0       7.0     21.1   86.0                                  150     1      0.0       7.1     21.0   88.0                                  150     3      0.0       7.2     22.2   86.0                                  150     10     0.0       7.5     23.2   86.7                                  150     20     0.0       7.1     22.4   88.7                                  ______________________________________                                         *Control                                                                 

                                      TABLE 5                                     __________________________________________________________________________    Treated Polyester (PET) Fiber Properties                                                                             Interfacial                                                                   Shear                                  Binder   % Solids                                                                           Breaking                                                                             Breaking                                                                              Tenacity                                                                           Modulus                                                                            Strength                                                                            Wetta-                           System   Pickup                                                                             Strength (kg)                                                                        Elongation (%)                                                                        (gpd)                                                                              (gpd)                                                                              (kg/cm.sup.2)                                                                       bility                           __________________________________________________________________________    1 (control)                                                                            --   7.66   21.4    7.7  88.5 6.67  5.0                              2.sup.1 (comparative)                                                                  1.1  8.48   21.8    8.2  97.3 7.20  4.0                              3.sup.2 (comparative)                                                                  0.28 --     --      --   --   7.10  8.5                              4.sup.3 (comparative)                                                                  0.15 7.80   20.3    7.8  98.2 7.49  3.0                              5.sup.4  0.20 8.07   20.0    8.1  98.9 7.30  8.5                              6.sup.5 (comparative)                                                                  0.18 8.16   21.5    8.2  94.0 7.06  6.0                              7.sup.6 (comparative)                                                                  0.44 7.98   19.0    8.0  88.5 7.57  6.5                              8.sup.7 (comparative)                                                                  0.37 7.80   19.9    7.8  88.8 --    4.0                              9.sup.8 (comparative)                                                                  0.45 8.03   19.7    8.0  87.8 --    4.0                              __________________________________________________________________________     .sup.1 Gammaglycidoxypropyltrimethoxysilane, water and oil (3.6, 67.5 and     28.9%); oil phase included (isohexadecylstearate, glycerol monooleate,        decaglycerol tetraoleate POE(15) tall oil fatty acid, sulfonated glycerol     trioleate, and POE(20) tallow amine (approximately 62.7, 5.9, 7.9, 7.8,       11.8 and 3.9%).                                                               .sup.2 Vinyl chloride copolymer.                                              .sup.3 Saturated polyester resin.                                             .sup.4 Gammaglycidoxypropyltrimethoxysilane, POE(9-10) octylphenol and        water (84.9, 0.1 and 15 percent, respectively).                               .sup.5 Isophthalic acid, trimellitic anhydride and diethylene glycol resi     in water.                                                                     .sup.6 Trimellitic anhydride and propylene glycol resin in water.             .sup.7 Unsaturated polyester resin in water.                                  .sup.8 Unsaturated polyester resin.                                      

                  TABLE 6                                                         ______________________________________                                        Wettability                                                                                                            Wetta-                               Binder         Contact   Ranking Aesthetic                                                                             bility                               System*                                                                              SEM     Angle (° 's)                                                                     1     2** Rating  Index                              ______________________________________                                        1      5       54        --   --   5       5.0                                2      5       59        --   --   3       4.0                                3      8       45        4    l    9       8.5                                4      3         81***   --   5    3       3.0                                5      8       41        1    2    9       8.5                                6      6       50        3    4    6       6.0                                7      6       66        2    3    7       6.5                                8      4       71        --   --   4       4.0                                9      4       69        5    --   4       4.0                                ______________________________________                                        *See TABLE 1 for details.                                                     **External evaluation of fibers with the five binder                          systems set forth wherein yarn was removed from a creel,                      passed through an isophthalic polyester resin (as in                          filament winding) bath under a roll partially submerged                       therein, passed through a slot stripper (to remove                            excess resin) and wound circumferentially on a flat                           mandrel. Tension was 5 pounds on each fiber.                                  Observations were as follows:                                                 Binder System                                                                 3         Fiber tended to fuzz before and                                               after resin bath. The fiber                                                   appeared to wet out almost                                                    immediately in bath.                                                4         No fuzz noted. Wet out almost as                                              fast as 3.                                                          5         No fuzzing noted when winding. The                                            fiber did not wet initially and                                               after winding the fibers still                                                appeared only partially wet out.                                    6         No fuzz noted. Appeared slightly                                              better than Binder 7. After wound,                                            appeared like 3.                                                    7         No fuzzing noted. Took a couple of                                            minutes to soak in. Wetted better                                             than Binder 5. After wound, appeared                                          like 3.                                                             ***Slightly modified formulation appears to give much                         better contact angle, i.e., about 40-50° .                         

                                      TABLE 7                                     __________________________________________________________________________    BMC Composite Properties for Fibers                                                                    Flexural                                                                             Tensile      Impact Strength                           Fiber Ratio                                                                         % Solids                                                                           Barcol                                                                             Strength                                                                             Strength                                                                             Shrinkage                                                                           (ft lbs/in)                      Binder System.sup.1                                                                    PET/Glass                                                                           Pickup                                                                             Hardness                                                                           (PSI × 100)                                                                    (PSI × 100)                                                                    (inches)                                                                            Notched                                                                            Unnotched                   __________________________________________________________________________    1 Control                                                                              100/0 --   34.8 6.22   3.31   0.0011                                                                              12.45                                                                              17.94                       2 Comparative.sup.4                                                                    100/0 1.1  42.6 5.52   3.45   0.0016                                                                              11.64                                                                              17.21                       3 Comparative                                                                          100/0 0.28 37.7 5.46   3.57   0.0013                                                                              12.96                                                                              18.28                       4 Comparative                                                                          100/0 0.15 39.5 6.35   3.30   0.0011                                                                              12.49                                                                              20.62                       5 Invention                                                                            100/0 0.20 41.2 6.24   3.50   0.0013                                                                              12.63                                                                              19.07                       6 Comparative                                                                          100/0 0.18 37.0 5.52   3.54   0.0010                                                                              13.12                                                                              20.68                       7 Comparative                                                                          100/0 0.15 37.4 5.32   3.49   0.0090                                                                              11.97                                                                              16.17                       8 Comparative                                                                          100/0 0.12 36.7 5.22   3.10   0.0014                                                                              10.86                                                                              19.12                       9 Comparative                                                                          100/0 0.15 37.2 5.15   3.45   0.0013                                                                              11.46                                                                              16.35                       10.sup.2 Comparative                                                                     0/100                                                                             --   47.1 13.17  8.63   0.0003                                                                               8.81                                                                              11.18                       11.sup.3 Comparative                                                                   0/0   --   42.2 2.60   0.95   0.0080                                                                               0.19                                                                               0.87                       1 Control                                                                              25/75 --   49.1 15.06  5.83   0.0099                                                                              18.28                                                                              25.21                       2 Comparative.sup.4                                                                    25/75 1.1  50.9 14.21  7.03   0.0055                                                                              16.86                                                                              25.96                       3 Comparative                                                                          25/75 0.28 48.6 15.01  6.62   0.0103                                                                              17.32                                                                              25.05                       4 Comparative                                                                          25/75 0.15 49.4 14.43  5.78   0.0098                                                                              16.52                                                                              23.28                       5 Invention                                                                            25/75 0.20 41.7 11.56  6.26   0.0079                                                                              15.72                                                                              23.00                       6 Comparative                                                                          25/75 0.18 49.0 13.76  6.94   0.0102                                                                              16.87                                                                              22.21                       7 Comparative                                                                          25/75 0.15 47.3 14.21  6.68   0.0106                                                                              17.75                                                                              25.45                       8 Comparative                                                                          25/75 0.12 45.8 14.53  6.10   0.0076                                                                              16.64                                                                              25.70                       9 Comparative                                                                          25/75 0.15 45.5 11.88  6.03   0.0078                                                                              15.78                                                                              21.28                       10.sup.2 Comparative                                                                    0/100                                                                              --   49.4 16.27  6.93   0.0003                                                                               8.81                                                                              11.18                       11.sup.3 Comparative                                                                   0/0   --   42.2 2.60   0.95   0.0080                                                                               0.19                                                                               0.87                       1 Control                                                                              50/50 --   43.3 10.17  5.47   0.0007                                                                               9.46                                                                              13.81                       2 Comparative.sup.4                                                                    50/50 1.1  47.0 8.84   5.41   0.0006                                                                              12.85                                                                              17.01                       3 Comparative                                                                          50/50 0.28 45.7 10.53  4.84   0.0005                                                                              11.44                                                                              15.63                       4 Comparative                                                                          50/50 0.15 42.5 8.48   4.64   0.0003                                                                              10.59                                                                              12.55                       5 Invention                                                                            50/50 0.20 41.5 9.91   5.36   0.0006                                                                              10.26                                                                              13.71                       6 Comparative                                                                          50/50 0.18 43.8 9.48   4.79   0.0003                                                                              12.00                                                                              14.59                       7 Comparative                                                                          50/50 0.15 45.1 10.84  5.27   0.0005                                                                              11.59                                                                              16.09                       8 Comparative                                                                          50/50 0.12 41.8 8.65   5.34   0.0010                                                                               9.77                                                                              12.32                       9 Comparative                                                                          50/50 0.15 43.3 11.58  4.62   0.0009                                                                               9.16                                                                              15.08                       10.sup.2 Comparative                                                                   0/100 --   47.1 13.17  8.63   0.0005                                                                              10.84                                                                              15.13                       11.sup.3 Comparative                                                                   0/0   --   42.2 2.60   0.95   0.0080                                                                               0.19                                                                               0.87                       __________________________________________________________________________

                                      TABLE 8                                     __________________________________________________________________________    Physical Properties of BMC Composites                                         Varying Resin Elongation                                                      Resin                  Notched                                                                            Unnotched                                                                           Flexural                                                                           Tensile                                Elongation,                                                                         PET/Glass                                                                           Barcol                                                                             Shrinkage                                                                           Impact                                                                             Impact                                                                              Strength                                                                           Strength                               Percent                                                                             Ratio Hardness                                                                           in/in ft lb/in                                                                           ft lb/in                                                                            psi  psi                                    __________________________________________________________________________    0.9.sup.1                                                                           0/100 60.7 0.0003                                                                              8.4  13.3  13 000                                                                             7210                                   0.9.sup.1                                                                           100/0 49.8 0.0050                                                                              14.8 24.3  4690 3140                                   1.8.sup.2                                                                           0/100 59.9 0.0004                                                                              7.6  10.4  11 300                                                                             6600                                   1.8.sup.2                                                                           12.5/87.5                                                                           60.0 0.0005                                                                              7.0  12.7  11 800                                                                             7050                                   1.8.sup.2                                                                           25/75 57.1 0.0001                                                                              7.8  12.9  9370 5710                                   1.8.sup.2                                                                           50/50 56.1 0.0010                                                                              12.0 12.9  8160 4640                                   1.8.sup.2                                                                           100/0 51.2 0.0044                                                                              14.8 23.0  4960 3310                                   6.1.sup.3                                                                           0/100 54.2 0.0004                                                                              8.0  10.7  14 400                                                                             8370                                   6.1.sup.3                                                                           12.5/87.5                                                                           51.5 0.0005                                                                              9.2  10.9  12 500                                                                             6570                                   6.1.sup.3                                                                           25/75 50.1 0.0004                                                                              9.3  16.5  9930 5670                                   6.1.sup.3                                                                           50/50 47.0 0.0016                                                                              11.6 17.2  8840 5410                                   6.1.sup.3                                                                           100/0 45.1 0.0021                                                                              16.1 26.6  5240 3480                                   10.sup.4                                                                            0/100 46.7 0.0003                                                                              6.6   8.0  13 400                                                                             7310                                   10.sup.4                                                                            12.5/87.5                                                                           47.7 0.0007                                                                              8.0  10.4  10 800                                                                             6090                                   10.sup.4                                                                            25/75 45.4 0.0006                                                                              8.4  10.8  10 600                                                                             6270                                   10.sup.4                                                                            50/50 44.1 0.0017                                                                              11.5 15.6  9900 4360                                   10.sup.4                                                                            100/0 33.0 0.0032                                                                              19.6 26.7  3970 3100                                   __________________________________________________________________________

                                      TABLE 9                                     __________________________________________________________________________     Physical Properties of PET/Glass                                             Fiber Reinforced Composites                                                                            Notched                                                                            Unnotched                                                                           Flexural                                                                           Tensile                              PET/Glass                                                                           Concentration,                                                                        Barcol                                                                             Shrinkage                                                                           Impact                                                                             Impact                                                                              Strength                                                                           Strength                             Ratio Percent Hardness                                                                           in/in ft lb/in                                                                           ft lb/in                                                                            psi  psi                                  __________________________________________________________________________     0/100                                                                              35      46.1 0.00020                                                                            16.3  20.5  17 700                                                                             6210                                  0/100                                                                              30      47.2 0.00039                                                                            13.6  19.3  17 200                                                                             5440                                  0/100                                                                              25      57.3 0.00056                                                                            10.0  15.4  11 100                                                                             7060                                  0/100                                                                              20      49.5 0.00057                                                                            11.9  17.5  20 800                                                                             5850                                  0/100                                                                              15      52.7 0.00108                                                                             8.2  14.6  15 300                                                                             5530                                  0/100                                                                              10      51.3 0.00123                                                                             7.6  11.5  11 900                                                                             6280                                 50/50 35      34.2 0.00149                                                                            17.3  27.7  11 000                                                                             5890                                 50/50 30      41.4 0.00151                                                                            16.5  22.9  10 900                                                                             5380                                 50/50 25      46.7 0.00087                                                                            14.9  19.3  13 000                                                                             4220                                 50/50 15      51.1 0.00155                                                                            11.2  15.5  12 600                                                                             4540                                 25/75 35      37.3 0.00045                                                                            17.0  22.8  13 800                                                                             7630                                 25/75 30      41.2 0.00059                                                                            17.2  22.9  15 800                                                                             5830                                 25/75 25      48.4 0.00067                                                                            14.6  18.8  13 100                                                                             6800                                 25/75 20      50.9 0.00064                                                                            12.8  17.0  14 300                                                                             7030                                 25/75 15      53.1 0.00121                                                                            13.5  16.0  14 200                                                                             5040                                 100/0 35      22.5 0.01072                                                                            21.2  24.8  5960 3540                                 100/0 30      29.8 0.01020                                                                            16.1  25.7  4550 4050                                 100/0 25      35.9 0.00937                                                                            20.9  27.4  5790 2980                                 100/0 20      40.1 0.00929                                                                            17.1  25.4  5810 3430                                 100/0 15      41.3 0.00877                                                                            13.4  19.1  4780 3340                                 100/0 10      46.8 0.00831                                                                             9.1  12.1  3640 2090                                 __________________________________________________________________________

                                      TABLE 10                                    __________________________________________________________________________     Composite Properties                                                                System =                                                                            Typical commercial polyester BMC formulation                                  20 weight percent glass loading, glass replaced                               by PET on equal volume basis                                                  Fiber length = 1/2 inch                                                         100%                                                                              25% PET/                                                                            50% PET/                                                            Glass                                                                             75% Glass                                                                           50% Glass                                                                           100% PET                                                                            ASTM                                     __________________________________________________________________________    Physical Properties                                                           Notched impact ft lb/in                                                                      9.1 12.0  11.6  16.9  D-256                                    Tensile strength GTH                                                                         6.9 7.0   5.4   3.5   D-638                                    PSI × 10.sup.3                                                          Compressive yield                                                                            16.6                                                                              --    14.2  10.0  D-695                                    Strength psi × 10.sup.3                                                 Flexural modulus                                                                             1.9 1.5   1.2   1.0   D-790                                    psi × 10.sup.6                                                          Tensile modulus                                                                              6.3 6.0   5.1   4.6   D-630                                    psi × 10.sup.5                                                          Abrasion - 1 K cycles                                                                        3.3 2.8   2.5   2.1   --                                       (gr)                                                                          Acid Resistance.sup.1 (25% H.sub.2 SO.sub.4                                   @ 200° C.)                                                             Percent tensile                                                                              28.7                                                                              --    14.4  6.5   --                                       strength loss                                                                 Electrical properties                                                                        189 --    192   197   D-495-73                                 arc resistance - seconds                                                      dielectric constant                                                           60 HZ          5.39                                                                              --    5.32  5.13  D-150-81                                 50 MHZ         5.11                                                                              --    4.92  4.81  D-150-81                                 1M HZ          4.90                                                                              --    4.79  4.60  D-150-81                                 __________________________________________________________________________     .sup.1 Typical commercial vinyl ester BMC formulation                    

                  TABLE 11                                                        ______________________________________                                        Nylon Fiber Reinforced Composites                                                             Fiber Ratio                                                                   Nylon 6/Glass                                                                 100/0  25/75    0/100                                         ______________________________________                                        Barcol Hardness   38.4     47.3     52.5                                      Impact Notched (ft lbs/in)                                                                      12.99    9.30     8.37                                      Impact Unnotched (ft lbs/in)                                                                    17.69    9.82     12.33                                     Flex Strength (PSI × 1000)                                                                5.38     12.28    14.60                                     Tensile Strength (PSI × 1000)                                                             2.76     5.13     5.32                                      ______________________________________                                    

What is claimed is:
 1. A high tenacity reinforcing polyester fiber forincorporation with a thermosetting resin which is then cured to form aplastic composite, said polyester fiber characterized in that the fiberis treated to enhance wettability with the resin and adhesion with thecured resin, and the fiber has a thermal shrinkage of 3 percent or less,a modulus after cure of at least 70 grams per denier and a tenacity ofat least 5.5 grams per denier.
 2. The fiber of claim 1 having anelongation of from about 10 to 28 percent and wherein the modulus aftercure is 70 to 90 grams per denier and the tenacity is 7 to 9 grams perdenier.
 3. The fiber of claim 1 which is polyethylene terephthalate. 4.A fiber reinforced plastic composite comprising a cured resin matrixreinforced with fiber, said fiber comprising a high tenacity reinforcingpolyester fiber that is treated to enhance adhesion with the curedresin, has a thermal shrinkage of 3 percent or less, a modulus aftercure of at least 70 grams per denier and a tenacity of at least 5.5grams per denier, said polyester fiber being present in an amountsufficient to provide improved notched impact strength to the composite.5. The composite of claim 4 wherein said cured resin matrix is formedfrom a thermosetting resin selected from the group consisting ofpolyester, epoxy, and vinyl ester.
 6. The composite of claim 5 whereinthe fiber has an elongation of from about 10 to 28 percent, a modulusafter cure of 70 to 90 grams per denier and a tenacity of 7 to 9 gramsper denier.
 7. The composite of claim 6 wherein said polyester fiber ispolyethylene terephthalate.
 8. The composite of claim 4 wherein theelongation of the fiber in the cured composite is at least 2 times thatof the resin matrix.